Organic semiconductors containing multi-heteroatom rings

Abstract

Oligomers of thiophene are ubiquitous in molecular materials research. Other ring systems, especially those lacking at least C2v symmetry are much less common. We investigated thiophene-thiazole, pyrrole-thiazole, thiophene-furan, and thiophene-selenophene co-oligomers, which nominally have the same conjugation length and physical dimensions as thiophene oligomers but contain a heteroatom, that should impact the electronic properties. The lower symmetry of the 1,3-thiazole system, among other attributes, makes these new systems chemically challenging to synthesize; however, the electronic and steric variability makes them interesting targets. One common method of synthesizing thiazole is the ring-closing reaction that generates an amino-substituted thiazole. We have done a systematic study to convert the aminothiazole to a more useful synthon using Sandmeyer conditions. We herein present the synthesis, characterization, and molecular or photoelectronic structures of selected mixed oligomer systems, along with a computational study to measure bond length alternation, localization indices, and HOMO-LUMO (band gap) energy. Aminothiazole can be deaminated using Sandmeyer conditions. As conjugation length increases with the addition of a more electron withdrawing group, there is a general decrease of the band gap as well as of the HOMO- LUMO energies.